Northstar Engines and System Technical Discussion Discussion, Spark plug replacment in Cadillac Engine Technical Discussion; Have 2003 DTS w/4.6, Vin (9) HO. just went over 100k and would like to replace spark plugs.
Have read ...

Spark plug replacment

Have 2003 DTS w/4.6, Vin (9) HO. just went over 100k and would like to replace spark plugs.
Have read a lot on about the plugs and have a few questions.
1. Stay w/ACDelco or can i try some other plug like NGK, Champion, Auto-lite ect?

2. If stay w/AC which one 41-987, 41-950 or Iridium?

3. It this as easy as they say it is, to change the plugs on a Northstar?

Re: Spark plug replacment

Your engine uses A/C Delco 41-987 plugs. Use them. You have no "wires". You have COP (Coil On Plug) ignition. Your plugs are under the ignition cassettes in the cam covers. Front one is easy. The rear, not so much.

Re: Spark plug replacment

noel, Stick with the OEM plugs. For your year they are probably AC Delco Professional Platinum brand, made by DENSO in Japan. (The stamping on the metal shell). Earlier cars had the same DENSO plug without the AC Delco brand.

Re: Spark plug replacment

Originally Posted by submariner409

noel, Stick with the OEM plugs. For your year they are probably AC Delco Professional Platinum brand, made by DENSO in Japan. (The stamping on the metal shell). Earlier cars had the same DENSO plug without the AC Delco brand.

Here's what you're looking at.

Thank you very much. i do have one more?. How many boot plugs are there. 1 per spark plug or one per engine. I order 8.

Re: Spark plug replacment

Yep - one per plug - it's another $45 down the tubes, but you'll be glad you don't need to go in there again. Get a tube of Dielectric Boot Grease at your local parts store and place an extra smear around the ceramic insulator of each plug before you torque it in.

You may find some oil on the plug metal shell and/or ceramic - not to worry. The plug wells are sealed with O-rings and they tend to weep over time. Oil is an insulator..............

Re: Spark plug replacment

The back ones are a bit tight. I did lose a 10mm ratcheting wrench to the deep depths of the engine when I was futzing around with the AIR check mounted back there and dropped the wrench. An air ratchet is helpful to getting those rear coil cassette bolts off, not a lot of room to turn a wrench.

Re: Spark plug replacment

Originally Posted by submariner409

Yep - one per plug - it's another $45 down the tubes, but you'll be glad you don't need to go in there again. Get a tube of Dielectric Boot Grease at your local parts store and place an extra smear around the ceramic insulator of each plug before you torque it in.

You may find some oil on the plug metal shell and/or ceramic - not to worry. The plug wells are sealed with O-rings and they tend to weep over time. Oil is an insulator..............

the front plugs and boot are in. had to stop because of the bracket over the back coil assembly. Is there an easy way to get the bracket off without putting the car on a lift?

Re: Spark plug replacment

Originally Posted by NHRATA01

The back ones are a bit tight. I did lose a 10mm ratcheting wrench to the deep depths of the engine when I was futzing around with the AIR check mounted back there and dropped the wrench. An air ratchet is helpful to getting those rear coil cassette bolts off, not a lot of room to turn a wrench.

Re: Spark plug replacment

That bracket is a pain to get off. I had a few of them off, I use a 10mm 1/4" drive socket, and a combination wrench. There are 3 bolts holding the bracket to the valve cover. One is buried in the back. Then there are 2 nuts threaded straight up to hold the valve to the pipe that goes to the exhaust manifold. After the 3 bolts and 2 nuts are off, you can lift the bracket and valve off, and swing the pipe out of the way. After you do a few, it does get easier.

Re: Spark plug replacment

ok job is done. Amazon had the 41-987 plugs ($6 x 8) and boots ($2 x 8). With tools it cost my be $150. To get to the 2 nuts holding the pipe to the bracket well i had to put the car on a lift. ALL cylinders looked good. no abnormal wear to the plugs.
Thanks for all the help it is easy except for the two nuts.